read text file: in visual c++ i am trying to execute program and nothing is display

[khalid_farooq]

/*
 * hello.c
 * This is a simple, introductory OpenGL program.
 */


#include<stdlib.h>
#include <GL/glut.h>
#include<iostream>
#include<fstream>

using std::fstream;
using namespace std;

void draw(void)
{
/* clear all pixels  */
	char fileName[] = "house1.txt";
	fstream instream;
	instream.open("c:/house1.txt",ios::in);
	if(instream.fail())
		return;
   glClear (GL_COLOR_BUFFER_BIT);
   GLint numstrip,numlines,x, y;
   instream>>numstrip;
   for(int j=0;j<numstrip;j++)
   {
	   instream>>numlines;
	   glBegin(GL_LINE_STRIP);
	   for(int i=0;i<numlines;i++)
	   {

		   instream>>x>>y;
		   glVertex2f(x,y);

	   }



   }

/* draw white polygon (rectangle) with corners at
 * (0.25, 0.25, 0.0) and (0.75, 0.75, 0.0)  
 */
   glColor3f (1.0, 1.0, 1.0);
  
   glEnd();

/* don't wait!  
 * start processing buffered OpenGL routines 
 */
   glFlush ();
}

void init (void) 
{
/* select clearing color 	*/
   glClearColor (0.0, 0.0, 0.0, 0.0);

/* initialize viewing values  */
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);
}

/* 
 * Declare initial window size, position, and display mode
 * (single buffer and RGBA).  Open window with "hello"
 * in its title bar.  Call initialization routines.
 * Register callback function to display graphics.
 * Enter main loop and process events.
 */
int main(int argc, char** argv)
{
   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
   glutInitWindowSize (640, 480); 
   glutInitWindowPosition (100, 100);
   glutCreateWindow ("hello");
   init ();
   glutDisplayFunc(draw); 
   glutMainLoop();
   return 0;   /* ANSI C requires main to return int. */
}

[gusano79]

The problem is in this line:

GLint numstrip, numlines, x, y;

You're declaring x and y as integer variables, but the values in your text file are decimals. Try declaring your variables like this:

GLint numstrip, numlines;
GLfloat x, y;

That got it to draw something for me.

Also: You're loading the contents of house1.txt inside your draw function. I can see how this makes the program simpler to write, but realize that it will open and read the file every single time the GLUT window needs to redraw itself--put some output to cout inside of draw if you're not sure what I mean there. It is much better practice to attempt to read the file only once, before you even initialize GLUT, and store its contents into a variable somewhere that draw can reference later.